What is “Treatment as Prevention”? Treatment as prevention is a broad term sometimes used to describe the potential prevention effect of treatment using antiretrovirals (ARVs). Since treatment lowers viral load in people with HIV, they may become less infectious and less likely to transmit HIV to their partners. Lower viral load in communities has been associated with lower rates of infection i, however, no randomized studies have demonstrated the effect of earlier treatment on prevention.
Under treatment guidelines operating in many parts of the world for the benefit of the infected patient’s individual health, people with HIV are not urged to start ARVs until their CD4 cell counts have dropped to a specific threshold such as 200, 250 or, perhaps more the consensus now, 350 CD4 cells. Other measures are also significant for individuals in deciding when to commence treatment such as their illness status, presence of co-infections, pregnancy in women or when their viral load exceeds a certain level.
Treatment-as-prevention advocates urge treating people earlier, either at higher CD4 cell count or without regard to CD4 count, to optimize the potential prevention impact. New evidence supporting this treat-early approach shows clinical benefits of ARV treatment for the infected individual at as high as a CD4 count of 350. Further studies are needed to look at the long term effects (benefits and adverse effects) of early initiation of treatment.
There are data from a growing number of population-wide observation studies, mainly in heterosexual populations, showing a correlation between successfully lowered viral loads and lower risk of transmission to others. Effective and reliably accessed ARV treatment can suppress HIV viral load to low or undetectable levels in an individual’s peripheral blood on a continuing basis. However, even when this indicator of effective treatment is achieved, the virus can be quantitated and measured in semen, in tissue or in other bodily reservoirs. Other data regarding individual partners experience is also encouraging and may yield important information applicable to men who have sex with men.
A novel and significant expansion of the strategy called “test and treat,” when integrated into coordinated national testing and drug distribution programs, has been proposed to help reduce population wide incidence rates of infection and curtail the epidemic and may be important to accomplish real reductions in HIV acquisition by healthy individuals who can have exposure risk from more than one partner.
Several investigators have modeled the potential effect of ARVs on HIV transmission based on the link between high viral load and HIV transmission. Using optimistic assumptions, the models have produced encouraging predictions about lowering HIV rates and even eliminating HIV transmission altogether.
Treatment as Prevention Investment Currently, the NIH is funding two trials examining the prevention effect of HIV treatment. The HIV Prevention Trials Network (HPTN) 052 Phase III trial is designed to determine the effectiveness of early treatment in preventing the sexual transmission of HIV in HIV-serodiscordant couples in eight countries in a 78-month study. The HPTN 065 trial will evaluate the feasibility, effectiveness and prevention effect of community-focused expanded HIV testing and linkage to care in the United States. In Europe, Imperial College London is planning an as-yet unfunded trial, entitled PopArt (Population effects of AntiRetroviral Therapy), which will determine the effect and feasibility of test-and-treat programs in South Africa. Finally, the ANRS has funded a study entitled TasP (Treatment as Prevention), to begin in 2010, which will examine the feasibility and acceptability of the test-and-treat concept in South Africa.